Separation and recovery of potassium salts from commercial nitrate of soda containing such salts.



TED STATES PATEN canton;

FRANCIS A. FREETH, OF GREAT CROSBY, AND HERBERT E. COCKSEDGE, OF LONDON,-

- ENGLAND. l

SEPARATION AND RECOVERY OF POTASSIUM SALTS FROM COMMERCIAL NITRATE 0F SODA CONTAINING SUCH SALTS.

No Drawing.

of Middlesex, England, respectively, have I invented certain new and useful Improvements in the Separation and Recovery of Potassium Salts from Commercial Nitrate of- Soda Containing Such Salts, of which the following is a specification.

We have discovered a process for separating and recovering in a marketable form the potassium nitrate which frequently occurs in commercial mtrate of soda, thereby 1ncreasm crude niter from which the sodium nitrate has been obtained.

The process is based upon the fact that the proportion of potassium to sodium present 1n an aqueous solution saturated with respect to both potassium and sodium nitrates is considerably greater at higher temperatures (for example temperatures in the neighborhood of 100 C.) than at lower temperatures (for example at temperatures in the neighborhood of 20 (1.).

The process consists essentially indigesting the crude nitrate of soda from which the potassium salts are tobe extracted with Water (or with wash waters from subsequent operations), the quantity of solvent liquor employed being such as will suflice to dissolve the whole of the potassium salts present in the crude nitrate of soda, and at the same time yield a solution saturated or nearly saturated with respect to potassium salts at the temperature at which the digestion was completed. I

The solution thus obtained is of course also saturated with respect to sodium nitrate at that temperature, but as only sufiicient solvent liquor isemployed to dissolve the potassium salts, the bulk of the sodium nitrate remains undissolved.

The solution is separated from the undis-' the value of the sodium nitrate from'w ich it has been extracted, inasmuch as the purified sodium salt will yield more nitric acid for a given weight of sulphuric acid employed than was the case with thesoda is conducted depends upon practical Specification of Letters Patent- Patented A 15, 1919,

Application filed February 12, 1917. Serial No. 148,292.

perature as that at which thedigestion was potassium salts, or if not completely satu-' rated, after concentration to saturationas subsequently described, is then diluted with sufficient water to keep the sodium nitrate 1n solution at the temperature to which the diluted solution is subsequently cooled. The" vsolution is then cooled to that temperature,

when potassium nitrate crystallizes out and is separated from the solution and washed toremove adherent mother liquor, being thus recovered in apure or practically pure form.

The process is fully described as follows The solubility of potassium nitrate in water and in an aqueous solution of sodium nitrate decreases as the temperature decreases, and the maximum temperature at which the digestion of the crude nitrate of considerations which are governed by the percentage of potassium salts in the crude nitrate of soda in the direction that, in order to obtain asufficient bulk of solution saturated or nearly saturated with respect a to potassium nitrate at the temperature of digestion to enable that solution to be separated from the undissolved sodium nitrate with reasonable facility, (that is, in order to avoid the production of a magma which is too thick and pasty) the digestion should be performed at a lower temperature when the percentage of potassium salts in the crude nitrate of soda is low than when that percentage is high.

The crude nitrate of soda containing potassium salts is digested. with water or With wash liquors obtained in a subsequent operation, preferably previously heatedto a temperature not exceeding 80 to 100 C., or to such lower temperature as may be necessary to enable the digestion to be completed at a temperature not exceeding that which is best adapted to give the required bulk of solution saturated or nearly saturated with potassium salts at that temperature and which, as previously explained, depends upon the percentage of potassium nitrate contained in the crude nitrate-:of-soda treatedr We may however raise the mixture of nitrate of soda and solvent liquor to the desired temperature by heating'after admixture instead of or, in addition to heating the solvent liquor before admixture.

Instead of using water for the digestion, we may employ the wash liquors which result from washing with water the sodium nitrate which remains undissolved when the digestion is completed, onthe wash liquors which resultfromwashing with water the sodium nitrate resulting from the subsequent concentration of the solution obtained by digesting the crude nitrate of soda, if and when such subsequent concentration is performed;'these wash liquors may be used either separately or together The'quantity of water or of Wash liquor emp1 yed for digestion isthat'which is suffioient oronly alittle more than sufficient to dissolve the potassium salts in the crude nitrate "of soda at the temperature at which the digestion is completed.

7, After digestion the solution is separated from the 'solidby any well-known means at as nearly as practicable the same tempera ture as that at which the digestion was.

finished. A solution is thus obtained es. nearly saturated with potassium nitrate as is practicable and; also saturated with. sodium 1 nitrate.

If the solution thus obtained is not saturated with respect to potasslum nitrate atthe desired temperature, it is concentrated until it is saturated with respect to potassium ni-. itrate at a high temperature (for example at 100 C.) ,and the sodium nitrate precipitated during the concentration is separated from the solution at, or approximately at that,

temperature.

Ifhowev-erthe digestion process has been carried out at 'a sufficiently high temperature, subsequent concentration is not required and the separation of sodium nitrate which occurs when this operation is performed is avoided.

The precipitated sodium nitrate may be trate with water may be subsequently em ployed' for the digestion of theicommercial nitrate of soda. 7 i

To the hot solution thus obtained, which is saturated with respect to potassium nitrate and sodium nitrate at a high temperature, from which any precipitated sod i um nitrate has been removed, water is added in such quantity that the ratio of water to sodium nitrate in the resulting solution the same or nearly the same as that which obtains in a solution saturated with respect to potassium and sodium nitrates at the temperature to which'the solution is to be subsequently cooled. "The resulting solution is then cooled to that temperature or approximately to that temperature when potassium nitrate crystallizes out, which, after removal from the motherliquor and washing with water orwith a solution of potassium nitrate, is pure or practically pure. c r g V Inasmuch as the mother liquor fromthis operation is saturated or nearly saturated with respect to both potassium and sodium nitrates atthe temperatures to which it was cooled, it -may be concentrated,until it is saturated or nearly saturated with respect to potassium nitrate at the temperature of concentration, the precipitated sodi-umni-v trate removed fromthe solution at that temperature, water-subsequently added to the solution, and the solution thus diluted cooled for, separation of potassium nitrate as described above, and thiscycle of operation. repeated indefinitely. I

The wash liquor resulting from the washingof the sodium nitrate which remains un-. dissolved after the digestion of the 'cOmm-en cial nitrate ofsoda, and/or. the wash liquor resulting-from thewashing of sodiumnitrate separatedout during thefloperationzof con centration may be if preferred, again concentrated until it is saturatedwith potassium nitrate, thesodium nitrate precipitated dun ing concentration removed from the solution,'water added tothe hot solution remaining until the ratio of water to sodium nitrate in the resulting solution is the same or nearly the same as that, which obtains in a solution saturated with respect to potassium and sodium nitrates at the temperature to which the solution is to be subsequently cooled, the'solution then cooled to that temperature, and the potassiumnitrate which crystallizes out from the solution removed and washed. .The wash liquor which results from the washing of the potassium nitrate may be trated solution cooled to this temperature,

when potassium nitrate crystallizes out,

which after washing with water or with a solution of potassium nitrate is pure or practically pure. 3

We declare that what we claim is 1. The processof separating potassium nitrate from commercial nitrate of soda which comprises extracting the potassium nitrate at an elevated temperature form of an aqueous solution, separating the solution from the undissolved sodium nitrate, adjusting the composition of said solution by dilution so that on cooling to a given lower temperature it will deposit a considerable amount of potassium nitrate without depositing sodium nitrate, cooling the solution to said lower temperature, and separating the potassium nitrate crystallizing therefrom.

2. The process of separating potassium nitrate from commercial nitrate of soda which comprises extracting the potassium nitrate at an elevated temperature by digestion with a relatively small quantity of water, separating the solution from the undissolved sodium nitrate, adjusting the composition of said solution by dilution so that on cooling to a given lower temperature it will deposit a considerable amount of potassium nitrate without depositing sodium nitrate, cooling the solution to said lower temperature, and separating the potassium nitrate crystallizing therefrom.

3. The process of separating potassium nitrate from commercial nitrate of soda which comprises extracting the potassium nitrate at an elevated temperature by digestion with a wash liquor obtained in the process, separating the solution from the undissolved sodium nitrate, adjusting the composition of said solution by dilution so that on cooling to a given lower temperature it will deposit a considerable amount of potassium nitrate without depositing sodium nitrate, cooling the solution to said lower temperature, and separating the potassium nitrate crystallizing therefrom.

4. The process of separating potassium nitrate from commercial nitrate of soda whichcomprises extracting the potassium nitrate at an elevated temperature by digestion with an aqueous liquid in amount suflicient to yield a solution substantially saturated with potassium nitrate at the temperature of digestion, separating the solution from the undissolved sodium nitrate, adjusting the composition of said solution by dilution so that on cooling to a given lower temperature it will deposit a considerable amount of potassium nitrate without depositing sodium nitrate, cooling the solution to said lower temperature, and separating the potassium nitrate crystallizing therefrom.

5. The process of separating potassium nitrate from commercial nitrate of soda which comprises extracting the potassium nitrate at an elevated temperature in the form of an aqueous solution, separating the solution from the undissolved sodium nitrate, adjusting the composition of said solution so that on cooling to a given lower temperature it will deposit a considerable amount of potassium nitrate without depositing sodium nitrate, said adjustment being performed by adding to the solution so much water that the solution will be saturated with sodium nitrate at the given lower temperature, cooling the solution to said lower temperature, and separating the potassium nitrate crystallizing therefrom.

6. The process of separating potassium nitrate from commercial nitrate of soda which comprises extracting the potassium nitrate at an elevated temperature in the form of an aqueous solution, separating the solution from the undissolved sodium nitrate, adj usting the composition of said solution so that on cooling to a given lower temperature it will deposit a considerable amount of potassium nitrate without depositing sodium nitrate, said adjustment being performed by concentrating the solution till it is saturated with potassium nitrate, removing the sodium nitrate which crystallizes out and adding enough water to keep the solution saturated with sodium nitrate at the given lower temperature, cooling the solution to said lower temperature, and separating the potassium nitrate crystallizing therefrom.

7. In a process for separating potassium nitrate from sodium nitrate, the step which consists in taking a solution which is nearly saturated with both salts at a low temperature, concentrating it till it is nearly saturated with potassium nitrate at a higher temperature, removing the precipitated sodium nitrate, adding water till the solution is not more than saturated with sodium nitrate at a given lower temperature, cooling to said lower temperature and removing the precipitated potassium nitrate.

8. The process of separating potassium nitrate from commercial nitrate of soda which comprises extracting the potassium nitrate at about 80 to 100 C. in the form of an aqueous solution, separating the solution from the undissolved sodium nitrate, adjusting the composition of said solution by dilution so that on cooling at about atmospheric temperature it will deposit a considerable amount of potassium nitrate with out depositing sodium nitrate, cooling the solution to said lower temperature, and separating the potassium nitrate crystallizing therefrom.

9. The process of separating potassium nitrate from commercial nitrate of soda which comprises extracting the potassium nitrate at an elevated temperature in the form of an aqueous solution, separating the solution from the undissolved sodium nitrate, adjusting the composition of said solution by dilution so that on cooling to a given lower temperature it will deposit a considerable amount of potassium nitrate without depositing sodium nitrate, cooling the solution to said lower temperature, and separating the potassium nitrate crystallizing therefrom, the elevated temperature and the volume of liquid for digestion being so chosen as to' avoid the production of a too pasty magma on digestionby obtaining a suflioient volume-of solution to enable said "5 solution to be separatedirom the undissolved sodium nitrate with reasonable facility. l

10. The process of separating potassium nitrate from mixtures of sodium nitrate and potassium nitrate which comprises extracting the potassium nitrate at an elevated temperature in the form of an aqueous solution, separating the solution from the undissolved sodium nitrate, adjusting the composition of said solution by dilution so that on coolcopies :of this patent may be obtained for five cents each, by addressing .the Commissioner if-Patents,

'in' to a iven lower tem erature it Will de- 1 b posit a considerable amount oi potassium .ni-

In Witness whereof, We have hereunto signed 'our names this 27 day of January 1917, in the presence of twosubscribing Witnesses. r 1

F. A. FREETH.

.H. E. OOGKSEDGE.

Witnesses: I

P. THo rsoN, J. MOLA'GHLAN.5

Washington. D. 0.

potassium nitrate 20 

